DRILLING WELLS FOR PILES
Drilling wells for piles is an auxiliary technology for arranging pile foundations in solid and incoherent, moisture-saturated soils, the implementation of which significantly increases the productivity of driving reinforced concrete piles.
HOW DO WE DRILL UNDER THE PILES?
Arrangement of wells for piles is carried out using self-propelled drilling rigs, which are equipped with equipment operating according to the technology of rotary rotary drilling – auger string. In the process of deepening the drill string into the ground, the worked-out soil rises to the surface of the well along the helical blades of the auger, after the well is developed to the design depth, the column is withdrawn from the excavation on a reverse run, and the finished well is used for further purposes – for driving reinforced concrete piles or forming rammed supports …
The peculiarities of the drilling technology depend on the soil conditions in which the work is carried out. If drilling is carried out on soft soils, the soil is excavated with a standard auger drill, without additional reinforcement. When drilling high-density soil, or soils with a large number of stony inclusions, the auger string is equipped with a carbide tip – a bit, which takes on the resistance of the soil and significantly increases the efficiency of driving hard rock.
If it is necessary to develop cohesive soils with a low density, which in the process of setting up a well crumble from the walls of the excavation to the bottom of the bottom, drilling is carried out using special solutions – bentonite, clay or polymer, which are pumped into the well by means of a compressor through a special pipe.
PILOT DRILLING TECHNOLOGY
The technology of drilling wells for piles is in demand in two cases – when it is necessary to drive driven piles in difficult conditions and when arranging rammed supports.
Drilling for driven piles is called leader drilling. Arrangement of leader wells is used in the following situations:
When driving piles into high-density soils with high resistance, which the pile cannot overcome under the influence of an impact hammer or vibrator;
When driving piles into solid frozen soil;
When driving piles into disconnected, moisture-saturated soils – swampy, silty soils and quicksands, the insufficient density of which does not allow accurate positioning of the pile to be submerged and leads to its deviations from the axis required by the project;
When driving reinforced concrete piles near existing buildings, in this case, leader wells allow avoiding dynamic loads on nearby foundations that arise during the operation of a diesel hammer.
Drilling for rammed piles is carried out when erecting pile foundations, in which not ready-made reinforced concrete products of industrial production are used as supports, but piles formed directly in the ground at the construction site. The process of their arrangement consists in developing a well of the required dimensions, immersing a reinforcing cage in the well and filling the excavation with a concrete mixture, as a result of which a full-fledged reinforced concrete support is created in the soil.
DRILLING FOR DRILLING PIECES
When drilling for rammed piles, wells are set up, the dimensions of which correspond to the design dimensions – the depth and diameter formed in the soil of the support. The drilling itself is carried out under the protection of a casing – a cylindrical steel structure, which is simultaneously used as a formwork for pouring concrete and prevents groundwater from entering the well and shattering its walls.
Drilling technology for rammed piles is implemented in the following sequence:
The drilling rig is located at the site of the well construction (the site is pre-marked) and drills to a depth of 2 meters;
The drill string is lifted and the first section of the casing is installed, after which the drill is inserted into the pipe and further development of the well is carried out;
The sinking of the casing is due to the development of the soil by the auger under its support end and the impact of pressing forces;
In the process of deepening the well, the casing sections are systematically increased (they are provided with sleeve or threaded connections);
After deepening the well to the design level, the auger string is withdrawn and the bottom of the bottom is cleaned by ramming, flushing with drilling fluid or blowing with compressed air;
The reinforcement cage is slinged, lifted and immersed inside the well using a boom crane;
A concrete-cast pipe is being installed, its lower part is placed at a distance of no more than 30 cm from the bottom of the well;
A concrete mixture is injected through the pipe into the well, while the pipe itself rises systematically as the well is filled with concrete;
Upon completion of concreting, the casing is removed from the well and the concrete is compacted by vibrating the mixture.
DRILLING TECHNOLOGY FOR DRILLING PIECES
The depth of the leader wells developed for the subsequent driving of reinforced concrete piles should be 1-1.5 meters less than the length of the submerged structure. The diameter is less than the cross-section of the pile trunk by 30-50 millimeters, depending on the density of the soil.
The leader drilling technology consists of the following stages:
Geodetic survey of the soil is carried out, aimed at establishing the density of the deep layers of the soil. The final decision on the need for leader drilling is made in the process of test pile driving, during which the effectiveness of the used pile driving hammers in a specific type of soil is determined;
Based on the characteristics of the soil of the construction site and the requirements for the dimensions of the leader wells, the drilling equipment suitable for the work is selected;
The pile field is broken down, drilling points are marked on the site;
Equipment is delivered to the facility and wells are drilled in the sizes required by the project;
Driving of piles into the leader wells is carried out sequentially with their drilling, since during the operation of a diesel hammer near an unclosed well, its walls may collapse;
Drilling of wells for piles is carried out with the help of MBU – mobile drilling rigs using rotary drilling technology. This technique is equipped on the basis of wheeled vehicles or tracked excavators, which are equipped with the appropriate drilling equipment.
Depending on the technological design, MBU are classified into:
Continuous auger drilling rigs equipped with a stackable drill string without an inner bore.
Installations for CFA drilling, which use a drill string with an internal cavity through which drilling fluid or concrete mixture is injected into the well.
Modern drilling rigs are capable of drilling wells for piles to a depth of 50 m, which makes it possible to immerse composite piles of the maximum possible size in them, the drilling diameter ranges from 100 to 800 mm.